Programme

I.1 -- Invited, VCTP-50

Date: Monday, 4 August 2025

Time: 09:20 - 10:00

Terahertz-Induced Plateau Extension in High-Order Harmonic Spectroscopy: Influence of Field Strength and Molecular Symmetry.

(a) Doan-An Trieu, (b) Cam-Tu Le, (c) Sang Ha, (d) Duong D. Hoang-Trong, (c) Van-Hoang Le, (c) Ngoc-Loan Phan

(a) Duy Tan University, Ho Chi Minh City, Vietnam; (b) Ton Duc Thang University, Ho Chi Minh City, Vietnam; (c) Ho Chi Minh City University of Education, Ho Chi Minh City, Vietnam; (d) Van Lang University, Ho Chi Minh City, Vietnam

We study the high-order harmonic generation (HHG) in the presence of terahertz (THz) fields, focusing on the function of spectral bandwidth versus THz strength. By solving the time-dependent Schrödinger equation for atomic and molecular targets under combined infrared and THz fields, we map the full evolution of HHG cutoff energies as a function of THz strength. The results show that moderate THz fields (about 5–20% of the laser strength) significantly extend the plateau, enabling generation of extreme ultraviolet photons with energies up to twice that of the THz-free case. We further analyze the role of molecular orbital symmetry in HHG efficiency by considering HCN and HNC molecules. The results reveal that σ-symmetry orbitals yield substantially stronger harmonics than π-symmetry ones. Bohmian trajectory analysis shows that electrons originating from π orbitals experience greater transverse drift, reducing their recombination probability and, consequently, the HHG yield. These findings highlight the combined roles of field engineering and molecular structure in controlling HHG processes for ultrafast light source development.

Presenter: Trieu Doan An